1. Technical Field
Example embodiments of the present invention relate in general to the field of an active scanning method, and more particularly, to an access point scanning method in a wireless LAN system.
2. Related Art
Various wireless communication technologies have been developed together with information communication technologies. One such wireless communication technology, a wireless local area network (WLAN), is a technology allowing wireless Internet access at a home or business or at a designated service providing region using a portable terminal, such as a personal digital assistant (PDA), a laptop computer and a portable multimedia player (PMP) based on wireless frequency technologies.
As standards for WLANs, Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards have been developed. IEEE 802.11a provides a transmission speed of 54 Mbps by using an unlicensed band of 5 GHz. IEEE 802.11b provides a transmission speed of 11 Mbps by using direct sequence spread spectrum (DSSS) at 2.4 GHz. IEEE 802.11g provides a transmission speed of 54 Mbps by using orthogonal frequency division multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmission speed of 300 Mbps with respect to two spatial streams by using multiple input multiple output (MIMO)-OFDM. IEEE 802.11n supports a channel bandwidth of 40 MHz at the maximum, and provides a transmission speed of 600 Mbps.
As the development of WLANs becomes more active and applications using WLANs are diversified, there is an increasing need for a new WLAN technology capable of supporting a throughput higher than that the data processing speed supported by IEEE 802.11n. WLAN technology for very high throughput (VHT) is one of the IEEE 802.11 WLAN technologies suggested to support a data processing speed of 1 Gbps or more. As one of the VHT WLAN technologies, IEEE 802.11ac is being developed as a standard for supporting a VHT at a frequency band of 5 GHz or below, and IEEE 802.11ad is being developed as a standard for supporting a VHT at a frequency band of 60 GHz.
In a system based on the above described WLAN technology, a station performing active scanning on multiple channels has difficulty identifying in which channel a desired access point is located, and thus sequentially performs the same scan on each of the multiple channels. That is, a station transmits a probe request frame on a channel, and receives probe response frames transmitted from access points during a maximum waiting time, and if the station fails to find a desired access point on the current channel, the station performs the same process on another channel.
Meanwhile, if an access point supports multiple channels and receives a probe request frame through a primary channel, the access point transmits a probe response frame in response to the probe request frame, but for a probe request frame received through a secondary channel, the access point does not respond and transmit a probe response frame.
In this environment, in order to find a desired access point, a station needs to scan a plurality of channels, which causes a great amount of time to be taken to find the access point.